Army finally advance at regular intervals (6)

I believe the answer is:

yearly

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'at regular intervals' is the definition.
I can't tell whether this definition defines the answer.

'army finally advance' is the wordplay.
'finally' indicates one should take the final letters.
'advance' becomes 'early' (similar in meaning).
The last letter of 'army' is 'y'.
'y'+'early'='YEARLY'

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(Other definitions for yearly that I've seen before include "A hundred times a century" , "Happening every twelve months" , "Perennial" , "on a regular basis" , "like circulation of the Sun?" .)

I've seen this clue in The Times.

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